Med Java

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== Null vs Undefined ======

**null** and **undefined** are both special values that indicate the absence of a value. However, they are used in slightly different contexts and have some differences in behavior.

===== Null =====

**null** is a value that represents **no value or no object**. \\ 
It is an assignment value that represents the ;;;intentional absence of any object value.;;; \\ 
You can explicitly assign null to a variable to indicate that the variable should have no value. \\ 
Comparing with **loose equality ==, null is equal to undefined.**

===== Undefined =====

**undefined** is a primitive value that indicates that **a variable has not been initialized**, and **no value has been assigned to it**. \\ 
When you declare a variable without assigning any value to it, it is **undefined**. \\ 
When you try to access an object property or an array element that doesn't exist, you get **undefined**. \\ 
Functions without a return statement return **undefined**.

===== Comparison =====

**null == undefined** returns **true**, as they are loosely equal.
**null === undefined** returns **false**, as they are not strictly equal (they are two different types). \\ 
Example:
<code javascript>
let a;
console.log(a); // undefined

a = null;
console.log(a); // null

console.log(null == undefined); // true
console.log(null === undefined); // false
</code>

===== Conclusion =====
  * Use **null** when you want to intentionally signify that there is no value.
  * **undefined** usually means that a variable has not been assigned a value, or a function is not returning anything. So it may be considered the unintentional absence of the value.